Bacillus thuringiensis is a Gram-positive bacterium that produces delta-endotoxins known as crystal proteins which are specifically toxic to certain orders and species of insects. Many different strains of B. thuringiensis have been shown to produce insecticidal crystal proteins. Compositions including B. thuringiensis strains which produce insecticidal proteins have been commercially available and used as environmentally acceptable insecticides.
As noted by Hofte et al., (1989) the majority of insecticidal B. thuringiensis strains are active against insect of the order Lepidoptera, i.e., caterpillar insects. Other B. thuringiensis strains are insecticidally active against insects of the order Diptera, i.e., flies and mosquitoes, or against both lepidopteran and dipteran insects. In recent years, a few B. thuringiensis strains have been reported as producing crystal proteins that are toxic to insects of the order coleoptera, i.e., beetles.
The dipteran-active Cyt toxins differ from most of the other B. thuringiensis insecticidal crystal proteins in that they are smaller and do not share conserved blocks of sequence homology. These proteins demonstrate broad cytolytic activity in vitro, yet are specifically toxic to larvae of dipteran insects in vivo. These properties have been described elsewhere (Chilcott and Ellar, 1988).
A number of genes encoding cytotoxic proteins have been cloned from several strains of B. thuringiensis. The review by Hate et al. (1989) discusses the genes and proteins that were identified in B. thuringiensis prior to 1990, and sets forth the nomenclature and classification scheme which has traditionally been applied to B. thuringiensis genes and proteins. cryI genes encode lepidopteran-toxic CryI proteins. cryII genes encode CryII proteins that are toxic to both lepidopterans and dipterans. cryIII genes encode coleopteran-toxic CryIII proteins, while cryIV genes encode dipteran-toxic CryIV proteins. A new nomenclature has been employed that systematically classifies the cry genes based upon DNA sequence homology rather than upon insect specificities (Crickmore, N. et al. Microbiol. and Mol. Bio. Rev. (1998) Vol. 62: 807-813; http://www.btnomenclature.info/).
The cloning and expression of a gene encoding a 26-kDa mosquitocidal toxin from the dipteran-active B. thuringiensis var. israelensis has been described (Ward et al., 1984), and the nucleotide sequence of this gene was reported (Ward and Ellar, 1986). The molecular mass of the toxin protein, CytA, calculated from the deduced amino acid sequence was determined to be 27,340 Da. The nucleotide sequence of the gene for a 27-kDa mosquitocidal Cyt protein isolated from B. thuringiensis var. morrisoni strain PG14 has been disclosed (Earp and Ellar, 1987). The sequence of this toxin protein was found to differ by only one amino acid residue from the CytIA protein of B. thuringiensis var. israelensis. 
The identification of a 25-kDa protein that exhibits cytolytic activity in vitro when activated by proteolysis from the mosquitocidal B. thuringiensis var. kyushuensis was described earlier (Knowles et al., 1992), and the nucleotide sequence of the gene for this protein, CytB, was reported (Koni and Ellar, 1993). The predicted molecular mass of the CytB protein is 29,236 Da and the deduced amino acid sequence is quite distinct, although it does share significant sequence similarity with the CytA protein of B. thuringiensis var. israelensis. 
The cloning and characterization of the gene for a 30-kDa toxin protein with activity on coleopteran and dipteran insects has been described (Intl. Pat. Appl. Pub. No. WO 95/02693, 1995). This gene, isolated from B. thuringiensis PS201T6, encodes a protein of 29,906 Da which exhibits a 64% sequence identity with the CytA toxin of B. thuringiensis var. israelensis. IRDIG17912 and the gene encoding it have little homology to the delta-endotoxins and genes of the prior art. IRDIG17912, which is a Cyt2-like toxin, demonstrates surprising insecticidal activity against insects of the order Coleoptera and Lepidoptera.
Despite the discovery of many selective protein toxins from B. thuringiensis, there remains a critical need to discover new, effective pest control agents that provide economic benefits to farmers, are capable of delaying or preventing the development of resistant insects, and are environmentally acceptable. Particularly needed are agents targeted to control a wide spectrum of economically important insect pests that effectively control insect populations that are, or could become, resistant to existing insect control agents and those with equal to or increased potency compared to currently deployed insecticidal protein toxins.